Polycyclic hydrocarbon compounds show non-aromaticity, have a stiff molecule, have a unique structure and accordingly are drawing attention in various fields. There are known, for example, diallyl adamantanedicarboxylate (JP 1988-100537 A) and adamantanedi(meth)acrylate derivatives (JP 1985-307844 A), each as a monomer for plastic lens superior in optical properties and heat resistance.
There are also known particular adamantane compounds having (meth)acryl group (JP 2000-327950 A and JP 2000-327994 A), as a monomer for coating composition superior in adhesivity, light resistance, chemical resistance and hardness or as a monomer for coating.
Meanwhile, in recent years, there has been a remarkable progress with respect to the light-emitting diode (hereinafter, abbreviated as LED) which is a semiconductor light-emitting device produced with a compound semiconductor. As the light-emitting material therefor, there were developed aluminum•indium•gallium•phosphorus (AlInGaP) for red to bitter orange color light and gallium nitride (GaN) for blue color light. There was also realized a near-ultraviolet LED of 400 nm or shorter (e.g. 365 nm or 370 nm).
There was also achieved a white LED by, for example, combining a fluorescent material with a blue LED or a near-ultraviolet LED.
LED has various advantages such as long life, high thermal stability, easy light control, low operating voltage and the like. Owing to the high evaluation of LED particularly for the high light-emitting efficiency and high reliability, active application of LED is being pushed forward in the fields such as display, display panel, vehicle lighting, signal lamp, mobile telephone, video camera and the like. As the package shape of LED, there have been developed various package shapes suited for applications, such as bullet-shaped lamp, surface mounting type and the like. With respect to, in particular, white LED, its application to lighting is being pushed forward and there is high expectation as an alternate light source for conventional incandescent lamp, halogen lamp, fluorescent lamp, etc. However, for the wide spread thereof, higher luminance and improved light source efficiency are needed.
Ordinarily, LED is encapsulated with a transparent encapsulant comprising an epoxy resin, a silicone resin or the like, in order to protect the semiconductor device accommodated inside. Of the materials for encapsulant, the epoxy resin, in particular, has high adhesivity and high handleablity, is inexpensive, and is a material suitable for practical use; therefore, it is in wide use for encapsulation of LED. Meanwhile, the encapsulant for LED is required to have high light resistance in association with the above-mentioned move of LED to shorter wavelength. Further, in association with the move of LED to higher luminance, the encapsulant for LED is strongly required to have high heat resistance capable of withstanding the heat generated by the LED element.
Conventional epoxy resins such as bisphenol A type glycidyl ether and the like, used as a component of encapsulant tend to be deteriorated owing to the move to shorter wavelength or the heat generation of LED device. Consequently, there is a problem that the resin gives rise to yellowing, inviting a reduction in LED luminance and a change in LED color tone.
Various investigations have been made in order to achieve the above tasks. For example, light resistance of resin was slightly increased by adding an alicyclic epoxy to a hydrogenated bisphenol A type glycidyl ether (JP 2003-73452 A). However, the resulting resin has no sufficient weather resistance practically and further has lower heat resistance, causing discoloration. Also, it was attempted to further add, to the resin, a phosphorus-based antioxidant. In this case, an effect of suppressing the discoloration caused by heat was seen but there was a reduction in light resistance.
With respect to polycyclic epoxy compounds, there is a case in which an epoxy compound having only one epoxy group, such as 1-adamantylglycidyl ether was produced; however, there is no case in which an epoxy compound having two or more epoxy groups was produced at a high yield at a high purity.
As the conventional process for producing 1-adamantylglycidyl ether, there is known a process which comprises reacting 1-adamantanol with epichlorohydrin in the presence of a catalytic amount of tin tetra-chloride and then allowing sodium hydroxide to act on the reaction product to obtain 1-adamantylglycidyl ether (The Journal of Organic Chemistry USSR, Vol. 27, No. 6, pp. 1089-1092, 1991).
The process gives a yield of 61% which is not bad. In this process, however, tin tetra-chloride (which is a Lewis acid) is used as the catalyst. For the safety reason of the catalyst, the solvent usable is limited to low-polarity solvents such as halides. Hence, in production of 1-adamantylglycidyl ether, when the starting raw material is changed from 1-adamantanol to an adamantanepolyol having two or more hydroxyl groups (which has very low solubility in low-polar solvents), the reactivity thereof is not certain. Further, there is a fear that epichlorohydrin itself polymerizes in the presence of an acid such as Lewis acid and the polymerizate remains as an impurity. As a process for obtaining a glycidyl ether from an alcohol, there is generally considered a process which comprises reacting an alcohol with an alkali metal or the like to synthesize an alcoholate and contacting the alcoholate with epichlorohydrin or epibromohydrin. However, there is no case in which this process has been applied to any polycyclic hydroxy compound having two or more hydroxyl groups.